P0579 Cruise control switch: reading or operation not right ("A")

By: Diagno editorial team · Updated: 2026-10-15

P0579 means: Cruise control switch: reading or operation not right ("A"). There is a fault in the cruise control or its switches. OK to drive, but have it checked soon. The most common repair costs about €50–100 in Estonia, depending on make and model. The most common cause: steering wheel switches or their wiring.

What it means

There is a fault in the cruise control or its switches. It doesn't harm the engine, but cruise control may not work. There is a signal, but the reading or operation isn't plausible. The cause may be the part itself or a real mechanical fault.

What you may notice

• Cruise control won't engage or drops out
• Engine light may be on

What could be wrong

1. 1Steering wheel switches or their wiring · Switch replacement €50–100
2. 2Brake or clutch pedal switch · Switch replacement €50–100
3. 3Speed sensor signal · Speed sensor replacement €90–180
4. 4Engine computer software · Control unit check and software €150–300

Repair difficulty: Easy

What you can check yourself

Check that the brake lights work properly. A faulty brake light switch often switches cruise control off. You can check the simple things yourself, but the repair is best done in a workshop.

How we fix it

1. We check the switch states on the diagnostic tool
2. We check the pedal switches and wiring
3. We replace the faulty switch

Standard SAE description: Cruise Control Multi-Function Input "A" Circuit Range/Performance